Method and apparatus for delivering a cased glass stream

ABSTRACT

Apparatus for forming a cased glass stream having an inner core glass surrounded by an outer casing glass that includes a spout for delivering core glass from a first source through a first orifice. A second orifice is vertically spaced beneath and aligned with the first orifice, and is surrounded by an annular chamber that communicates with the second orifice through a gap between the first and second orifices. A tube delivers casing glass from the outlet opening of a casing glass spout to the annular chamber in such a way that glass flows by gravity through the orifices from the first and second sources to form the cased glass stream. A hollow tube within the casing glass spout is positioned with respect to the spout outlet opening for metering flow of casing glass through the outlet opening and delivery tube to the annular chamber surrounding the orifices. The interior of the hollow tube is coupled to a source of gas under pressure so as to maintain the tube interior, and the interior of the thin fall of casing glass through the spout outlet opening, at a pressure above ambient pressure surrounding the casing glass spout. This elevated gas pressure within the casing glass fall reverses the pressure differential between the interior and exterior of the spout outlet opening, so that any tendency for air to migrate through the refractory material surrounding the outlet opening and into the casing glass fall is eliminated.

This application is a division of application Ser. No. 09/699,539 filedOct. 30, 2000, now U.S. Pat. No. 6,622,525, which is a division ofapplication Ser. No. 09/252,400 filed Feb. 18, 1999, now U.S. Pat. No.6,176,103, which is a division of application Ser. No. 08/903,785 filedJul. 31, 1997 and now abandoned.

BACKGROUND AND OBJECTS OF THE INVENTION

The present invention is directed to delivery of a glass stream forforming glass charges for glassware manufacture, and more particularlyto a method and apparatus for delivering a so-called cased glass streamin which an inner or core glass is surrounded by an outer or casingglass.

It has heretofore been proposed to provide a cased glass stream forforming glassware having layered wall segments. U.S. application Ser.Nos. 08/374,371 and 08/374,372 disclose techniques for delivering such acased glass stream in which core glass from a first source is deliveredthrough a first orifice. A second orifice is vertically spaced beneathand aligned with the first orifice, and is surrounded by an annularchamber that communicates with the second orifice through a gap betweenthe first and second orifices. A heated tube delivers casing glass froma second glass source to the annular chamber that surrounds the secondorifice. Glass flows by gravity through the first and second orificesfrom the first and second sources in such a way that a cased glassstream emerges from the second orifice. This cased glass stream may besheared by conventional techniques to form individual cased glass gobsfor delivery to conventional individual section glassware formingmachines.

Although the techniques disclosed in the noted patent applicationsaddress and overcome problems theretofore extant in the art, furtherimprovements remain desirable. For example, the presence of air bubbles,sometimes termed “blisters,” in the casing glass stream has been aproblem. Flow of casing glass from the casing glass spout is controlledby a spout tube, which is positioned over the casing glass spout outletopening so as to meter casing glass flow at the desired volumetric ratiorelative to core glass flow. However, the volumetric ratio of casingglass flow to core glass flow is very low, such as on the order of 5 to10%. Consequently, when using conventional glassware forming equipment,the extremely low volume of casing glass flowing through the casingglass spout outlet forms a thin fall, around one-quarter inch thick,around the outlet opening and around the upper portion of the heateddelivery tube, with the volume within this fall being open. After aperiod of operation, air bubbles or blisters begin to appear in thecasing glass stream. It is believed that a chimney-like effect of theheated air within the interior of the spout outlet opening and theinterior of the casing glass delivery control tube creates a pressuredifferential or gradient between the ambient atmosphere outside of thecasing glass spout and the interior within the thin glass fall. It isbelieved that this pressure gradient promotes migration of air throughthe refractory material of the casing glass spout, and eventually intothe thin glass fall within the spout outlet.

A number of techniques have been proposed in an effort to eliminate thisair bubble or blister problem, including lining of the spout outletopening with platinum in an effort to block air migration. The techniquethat is currently preferred is periodically to “flood” the casing glassoutlet and heated delivery tube with casing glass far in excess of thatneeded for forming the cased glass stream, and to maintain thisexcessive casing glass flow for a period of time. It is believed thatthis “flooding” of the casing glass delivery path eliminates the chimneyeffect previously described, and further that hydrostatic pressure onthe casing glass promotes flow of casing glass into the refractorymaterial of the spout outlet opening so as to block air migration paths.When casing glass flow at reduced level is resumed, the air bubbles orblisters are eliminated for a period of time. However, continued use ofthe ceramic spout requires that the described “flooding” operation beundertaken with increasing frequency, apparently due to increasingerosion and wear of the spout material. It is believed that, as therefractory spout material ages, it becomes more difficult to fill theair migration cracks and passages within casing glass spout. In anyevent, the described “flooding” operation detracts from glassproduction, and therefore undesirably increases production costs.Furthermore, production of cased glass having air bubbles or blisters inthe casing layer results in undesirably increased scrap rates, furtherincreasing production costs.

It is therefore a general object of the present invention to provide amethod and apparatus for delivering a glass stream, particularly a casedglass stream, in which formation of air bubbles or blisters in the thinglass fall of the casing glass stream is reduced or eliminated, and inwhich the need periodically to “flood” the glass stream delivery path isalso eliminated. Another and related object of the present invention isto provide a method and apparatus for delivering a glass stream,particularly a cased glass stream, that is characterized by improvedproduction efficiency and therefore reduced manufacturing cost ascompared with similar prior art techniques.

SUMMARY OF THE INVENTION

Apparatus for forming a cased glass stream having an inner core glasssurrounded by an outer casing glass in accordance with a presentlypreferred embodiment of the invention includes a spout for deliveringcore glass from a first source through a first orifice. A second orificeis vertically spaced beneath and aligned with the first orifice, and issurrounded by an annular chamber that communicates with the secondorifice through a gap between the first and second orifices. A tubedelivers casing glass to the annular chamber from the outlet opening ofa casing glass spout in such a way that glass continuously flows bygravity through the orifices from the first and second sources to formthe cased glass stream. A hollow spout tube within the casing glassspout is positioned with respect to the spout outlet opening formetering flow of casing glass through the outlet opening and deliverytube to the annular chamber surrounding the orifices. The interior ofthis spout tube is coupled to a source of gas under pressure so as tomaintain the tube interior and the interior of the thin fall of casingglass through the spout outlet opening at a pressure above ambientpressure surrounding the casing glass spout. This elevated gas pressurewithin the casing glass fall reverses the pressure differential betweenthe interior and exterior of the spout outlet opening, so that anytendency for air to migrate through the refractory material surroundingthe outlet opening and into the casing glass fall is eliminated.

In accordance with another aspect of the present invention, there isprovided an apparatus for delivering a glass stream that includes aglass spout having a lower outlet opening and a flow control spout tubedisclosed within the spout. The spout tube has a closed upper end, ahollow interior and an open lower end adjacent to the spout outletopening, and position of the tube within the spout is controlled so asto control flow of glass through the outlet opening. The hollow interiorof the flow control tube is coupled to a source of gas under pressure soas to maintain the tube interior at a pressure above that of ambient airsurrounding the spout. Thus, a third aspect of the inventioncontemplates a method of preventing permeation of air through therefractory material around the spout outlet opening into the glassflowing through the outlet opening by delivering gas under pressure tothe flow control tube so as to maintain gas pressure within the tube andwithin the spout outlet opening above ambient air pressure around thespout. By way of example, gas pressure within the flow control tube andthe spout outlet opening may be maintained at a pressure of about twoinches of water column above ambient. The gas maintained under pressurewithin the spout tube may comprise air, nitrogen or argon. In someapplications, such as manufacture of amber glass, it may be desirable toprovide a reducing gas within the spout tube and in contact with theglass flow, which would thus advantageously change the nature of theatmosphere in contact with the glass flow. For example, methane oranother combustible gas may be injected into the spout tube to bum andmaintain a reducing atmosphere at elevated pressure in contact with theglass flow.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with additional objects, features and advantagesthereof, will be best understood from the following description, theappended claims and the accompanying drawings in which:

FIG. 1 is a fragmentary elevational schematic diagram of a glassdelivery system in accordance with a presently preferred embodiment ofthe invention;

FIG. 2 is a fragmentary sectional view on an enlarged scale of a portionof the delivery system illustrated in FIG. 1;

FIG. 3 is a fragmentary sectional view on an enlarged scale of anotherportion of the glass delivery system illustrated in FIG. 1; and

FIG. 4 is a sectional view similar to that of FIG. 3 but showing amodified embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The drawings illustrate a system 10 for delivering a stream of casedglass. A first forehearth 12 delivers core glass to a bowl or spout 14that has an opening 16 at the lower end thereof. Spout 14 is surroundedby a protective casing 18, preferably constructed of nonmagneticmaterial such as stainless steel. A spout tube 20 and a plunger 22control delivery of core glass from spout 14 through opening 16 to andthrough one or more first orifices 24 carried by an upper orifice ring26 beneath spout 14. A lower orifice ring 28 carries one or more secondorifices 30 positioned beneath orifices 24 and axially alignedtherewith. Orifice(s) 30 is surrounded by an annular chamber 32 formedbetween orifice rings 26, 28. Chamber 32 communicates with orifice(s) 30by means of a lateral space or gap between orifices 24, 30. Annularchamber 32 is coupled by a delivery tube 34 to the opening 36 at thelower end of a casing glass spout 38. Spout 38 includes a deliverycontrol spout tube 40, and is coupled to a casing glass forehearth.Delivery tube 34 is, resistance-heated by control electronics 41 formaintaining flow of casing glass to chamber 32. To the extent thus fardescribed, system 10 is essentially the same as disclosed in above-notedU.S. application Ser. Nos. 08/374,371 and 08/374,372. The former suchapplication is directed in particular to construction of casing glassdelivery tube 34, while the latter of such applications is directed inparticular to construction of orifice rings 24, 26. The disclosures ofsuch applications, both of which are assigned to the assignee hereof,are incorporated herein by reference for purposes of background.

A characteristic of cased glass stream delivery systems is that thevolumetric ratio of casing glass to core glass is extremely low, whichis to say that the quantity of casing glass needed per unit volume ofcore glass is extremely low. Consequently, casing glass flow rate isextremely low, and does not fill the volume of either delivery tube 34or spout outlet opening 36. As shown in greater detail in FIG. 2, thelow volumetric flow rate of casing glass is such that the glass thatcontinuously flows beneath the lower open end of spout tube 40 throughspout outlet opening 36 and into the upper end of delivery tube 34 formsa thin wall or fall around the conical interior of opening 36 into theinterior of tube 34. In current systems for commercial production ofcasing glass, this thin layer or fall of casing glass 42 around theinterior of the conical interior of outlet opening 36 is aroundone-quarter inch thick. This thin fall continues into tube 34, which isdisposed at an angle to the axis of opening 36. The glass that initiallytends to flow along the upper surface of tube 34 eventually breaks awayfrom the tube surface, forming a fall 44 that merges into a thin flow 46that flows along the angulated lower surface of tube 34. The flows 42,44, 46 are continuous, smooth and laminar, and do not fold uponthemselves which would tend to trap air bubbles. Consequently, it isbelieved that a “chimney effect,” caused by the heated air within tube40, glass fall 42 and glass falls 44, 46, creates a pressure gradient ordifferential with respect to the external atmosphere, which promotesmigration of air through the refractory material of spout 38 surroundingoutlet opening 36. This air migration eventually reaches the interior ofthe refractory material, and results in bubbles or blisters within fall42.

To overcome this effect, the present invention contemplates that asource of gas under pressure be coupled to the open interior of spouttube 40, outlet opening 36 and tube 34. Specifically, a cap 50 is placedover the upper end of tube 40. A hollow tube 52 extends upwardly fromcap 40, and is surrounded at its upper end by a tube 54 of largerdiameter. Thus, tubes 52, 54 effectively form a rotary union 56 thatpermits both rotation of tube 40, and vertical motion of tube 40 bymeans of bracket 58 for controlling the flow-metering gap between theopen lower end of tube 40 and the upper end of outlet opening 36. Rotaryunion 56 is coupled by a conduit 59 to a blower 60, which continuouslysupplies gas under pressure (ambient air in this embodiment) throughconduit 59 and union 56 to the hollow interior of tube 40. A gauge 62 iscoupled to union 56 for monitoring air pressure within tube 40. An airdeflector 64 is externally positioned around tube 52 beneath union 56 toprevent direct impingement of air upon cap 50, which would unduly coolthe glass within spout 38.

The presence of gas under pressure within tube 40 and outlet opening 36splits fall 44 (FIG. 2) and fills the upper interior of tube 34 withair. However, because tube 34 is of metal composition, preferablyplatinum, migration of air through the ceramic insulating materialsurrounding tube 34 is not a problem. Rather, it is the elevated airpressure within outlet opening 36 that effectively cancels the “chimneyeffect” formerly extant, and reverses the pressure differential orgradient across the ceramic material surrounding the spout outlet.Creation of air bubbles or blisters within the casing glass material issubstantially eliminated. It has been found that gas pressure withintube 40 and outlet opening 36 in the range of about 0.05 to 10 inches ofwater column above ambient air pressure, and most preferably about twoinches of water column above ambient air pressure, yields satisfactoryresults.

As noted above, FIGS. 1-3 illustrate a presently preferred embodiment inwhich the injected gas is air. However, other gases may be employed forobtaining other desirable effects. FIG. 4 illustrates a system in whichthe rotary union 56 a includes a tube 70 for connecting an external gassource 72 to the interior of tube 56. The gas from source 72 maycomprise nitrogen or argon, for example. In the manufacture of amberglass, for example, it would be desirable to maintain a reducing oroxygen-lean atmosphere within spout tube 40 in contact with the glassfall to prevent oxidation of the glass. For this purpose, gas source 72may comprise a source of methane or other combustible gas. Combustion ofsuch gas within the upper volume of tube 40 will produce the desiredreducing atmosphere while maintaining elevated pressure to avoid gasmigration through the spout material.

1. Apparatus for delivering a glass stream comprising: a glass spouthaving a lower outlet opening, a spout flow tube disposed within saidspout, said tube having a closed upper end, a hollow interior and anopen lower end disposed adjacent to said spout outlet opening, means forcontrolling position of said tube lower end with respect to said outletopening for controlling glass flow through said outlet opening, and asource of gas at continuous elevated pressure coupled to said interiorvolume of said tube, and through said tube to said opening, continuouslymaintaining said interior volume of said tube at a pressure aboveambient pressure surrounding said spout.
 2. The apparatus set forth inclaim 1 wherein said outlet opening is conical, and wherein said tube ispositioned with respect to said outlet opening so that glass exitingsaid opening forms a film of glass extending around said conicalopening, the interior of said film being pressurized from said tube. 3.The apparatus set forth in claim 2 further comprising a rotary unionconnecting said source to said closed upper end of said tube.